SummaryPedigree structures of 161 uncle/niece-aunt/nephew and 4420 first cousin consanguineous marriages registered during the 19th and 20th centuries in two large and very different Spanish regions have been analysed and their genetic consequences evaluated. The frequencies of the different pedigree subtypes within each degree of relationship were quite similar in both populations despite significant heterogeneity in inbreeding patterns. The mean X-linked inbreeding coefficient (Fx) for each type of cousin mating was calculated and compared to that expected for autosomal genes (F). The effect of genealogical structure on theFx/Fradio was compared to different cultural populations worldwide. Preferentiality and avoidance of close consanguinity along with specific types of pedigrees are discussed on the basis of premarital migration and sociocultural rules still deeply rooted in certain human groups. By admitting that the observedFxcoefficient is usually higher thanFin most human populations some remarks have been made in terms of population genetic risk.
Record linking provided information on the complete reproductive schedules of a sample of 1102 couples with at least two children born alive from a rural Spanish community characterised by very high extramarital reproduction. Birth spacing was analysed considering final family size as well as the legitimate-illegitimate status and sex of the newborn, and survival of the preceding sibling.
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